Four Citigroup Inc. executives who bought the bank’s stock last week generated a $2.2 million paper profit within nine days, regulatory filings show.

The executives, including director Roberto Hernandez, benefited as the company’s stock climbed 47 percent from March 10 through yesterday’s close of markets, after Chief Executive Officer Vikram Pandit said in a memo that the bank is having the best quarter since 2007. Their buying spree was the first by bank insiders since Jan. 14, filings show.

“You’re supposed to buy when everyone else is selling,” said Bruce Foerster, a former Lehman Brothers Holdings Inc. managing director who now runs South Beach Capital Markets in Miami. Banks have internal systems to monitor executive trades and prevent abuses, he said.

Pandit wrote in the internal memo March 10 that the company was profitable in January and February, leaving him “encouraged with the strength of our business so far in 2009.” The comments triggered Citigroup’s biggest one-day percentage gain since Nov. 24, spurring global markets.

They just lucked out when the "internal memo" somehow leaked this week, leading to a monster rally in the financials.